Prefix-Adaptive Block Diffusion for Efficient Document Recognition

Mingxu Chai, Ziyu Shen, Chenyu Liu, Jihua Kang, Tao Gui, Qi Zhang


Abstract
Block Diffusion Models (BDMs) support parallel generation, flexible-length output, and KV caching, making them promising for efficient document parsing. However, existing BDMs bind denoising and cache commitment to fixed block boundaries: parallelism shrinks during intra-block denoising, while generated tokens cannot be cached until the whole block is completed. Moreover, intra-block bidirectional denoising conflicts with inter-block autoregression, creating inconsistent information flow that can challenge structure-sensitive recognition. We propose the Prefix-Adaptive Block Diffusion Model (PA-BDM), which replaces intra-block bidirectional denoising with causal denoising from prefix to suffix and treats the block size as a maximum candidate range rather than a fixed commitment unit. PA-BDM uses Confidence-gated Structural Loss (CSL) to build low-entropy prefixes before extending training to longer continuations. During inference, Progressive Prefix Commitment (PPC) then dynamically commits the longest reliable prefix into the KV cache and resets the next candidate range from the updated prefix, restoring a large parallel decoding space at each step. Experiments show that the 3B PA-BDM achieves higher recognition scores on several benchmarks and improves inference throughput by 71.6% over the 2.5B MinerU-Diffusion.
Anthology ID:
2026.emnlp-main.870
Volume:
Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
EMNLP
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
20124–20138
Language:
URL:
https://aclanthology.org/2026.emnlp-main.870/
DOI:
Bibkey:
Cite (ACL):
Mingxu Chai, Ziyu Shen, Chenyu Liu, Jihua Kang, Tao Gui, and Qi Zhang. 2026. Prefix-Adaptive Block Diffusion for Efficient Document Recognition. In Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing, pages 20124–20138, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Prefix-Adaptive Block Diffusion for Efficient Document Recognition (Chai et al., EMNLP 2026)
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PDF:
https://aclanthology.org/2026.emnlp-main.870.pdf